Hard Drive Performance Wiki

[Duwelon]

I want to make this post so we can collect information on Hard Drives in one easy to read thread about what factors impact hard drive performance and in what way. I don't know too much about hard drives other than the impact of RPM and platter density, and maybe the cache on them.

Let me start by posting what I know, which may need correction and will definately need additional information.

RPM : Determines seek time, max sustained read/write speed. Higher RPM results in increased power usage, heat, noise, and in the long run a shorter life.

Capacity : Capacity has a large impact on performance. The determining factor in the performance of a hard drive as far as capacity goes is the density of the data on each hard drive platter. A drive with 320GB per platter will have better performance than another drive with 160GB per platter, assuming the RPM is the same. That all said, higher platter density (and higher capacity drives in general) results in higher sustained read times.

Are 4 platters better than 2 platters when the density and RPM are exactly the same?

Does a higher platter density impact other factors like seek time?

Cache : The more Cache is available for the drive to use, the higher the chance that the data your OS or apps need will be available in the cache so that it doesn't have to read from the disk and incur the resulting penalties.

What determines a drive's burst?

How about minimum read/write speeds?

What makes a hard drive better in RAID configurations (in terms of performance) than others?

 

[GarfieldtheCat]

Originally posted by: Duwelon
RPM : Determines seek time, max sustained read/write speed. Higher RPM results in increased power usage, heat, noise, and in the long run a shorter life.

Read/write speed is based on both RPM and platter density.

Capacity : Capacity has a large impact on performance. The determining factor in the performance of a hard drive as far as capacity goes is the density of the data on each hard drive platter. A drive with 320GB per platter will have better performance than another drive with 160GB per platter, assuming the RPM is the same. That all said, higher platter density (and higher capacity drives in general) results in higher sustained read times.

Capacity and density are two separate things. Density is the important one.

Are 4 platters better than 2 platters when the density and RPM are exactly the same?

Technically yes, but from what I have read and seen, it's on the order of a few percent, so it isn't really that big of a deal.

Does a higher platter density impact other factors like seek time?

It can, higher density means a smaller surface area on the platter, which means the actuator arm has to be more precise to read the correct spot.

Cache : The more Cache is available for the drive to use, the higher the chance that the data your OS or apps need will be available in the cache so that it doesn't have to read from the disk and incur the resulting penalties.

Yes, and the algorithm used to determine what goes in the cache is important too.

What determines a drive's burst?

I think it's based on the read speed of the cache

How about minimum read/write speeds?

Based on the density of the platters. From the outside in, each track can only hold so much data. The inner tracks have to use a lower linear density, so the inner tracks read/wrtie slower then the outer. All HD's have to do this, just like CD or DVD writers can't burn at full speed throughout the entire disk.

What makes a hard drive better in RAID configurations (in terms of performance) than others?

RAID 0 will double your STR, since the data comes off of two disks instead of one. It doesn't help access time though (or disk latency). So RAID 0 doesn't help most applications, and double your chance for losing your data. If you are accessing small amounts of data, the limiting factor will be access time and latency, not STR.


To understand HD speed, things like access time, cache size, RPM, and platter density are all specific measurable items, but they don't equal real world performance. Just like with CPU speeds, a 3GHz Q6600 doesn't equal a 3GHz Q9450. The Q9450 has slightly higher performance, so "clock for clock", the chips aren't equal.

The big determination for HD speed is the firmware. Good firmware will make the HD faster, poor firmware will make it look really bad. That is why you see the new SCSI and SAS server drivers (running at 10K and 15K rpm) losing to fast SATA drives. Their firmware isn't really bad in this case, it's just optimized for server (multi-user) use, not desktop.